The Telemetry

Information about key aspects of Challenger's 75-second flight is stored on computer tapes and may give NASA investigators evidence needed to pinpoint the cause of the explosion.

Called telemetry data, the information is radioed to Earth so quickly that investigators will have to replay the tapes in ultraslow motion to search for any millisecond aberration in the shuttle's performance.

Tapes from two shuttle antenna stations at Ponce Inlet in Volusia County and Merritt Island in Brevard County have been sent to NASA headquarters in Washington for analysis, said space agency spokesman George Diller. Copies also are at Kennedy Space Center and Johnson Space Center in Houston, he said. The tracking stations are part of a network of antennas and satellites designed to receive and send information about the shuttle during its ascent and while it is in orbit.

In a sense, the data is similar to that stored in a black box on an airliner, but thousands of times more detailed.

Aspects of the shuttle's performance, such as fuel flow and pressure in each tank and line, engine thrust, speed and altitude, are monitored by a complex system of five computers, 300 electronic boxes and hundreds of miles of electrical wiring.

Thousands of functions are monitored and simultaneously radioed back to Earth each second. One monitoring system measures only the shuttle's main engines and another the remainder of the spaceplane's functions.

This information is relayed to Kennedy Space Center, which monitors the liftoff, and to Johnson Space Center, which monitors the shuttle when it is in orbit. After the shuttle reaches orbit, telemetry data is sent only to Houston.

Some functions are monitored as often as 25 times each second, too fast for humans to keep up with. So during launches, the fastest that new information is flashed on computer terminal screens is every second.

Information is coming in so fast that some is stored on tape for later review.

NASA officials say that telemetry data flashed on screens appeared normal until the explosion. Tapes of this data will be replayed in slow motion to check for any unusual readings that happened so quickly they did not appear on monitor screens.

After a normal flight, it usually takes from three to four weeks to compile all telemetry data and file a flight report, said NASA spokesman Jerry White. Another agency spokesman, John Lawrence, said the Challenger telemetry review will take longer because NASA has ''never looked at a mission in this detail before.''

Information from the tapes will be compared with information from past Challenger launches and engine tests, Lawrence said.